Recovery of hydrocarbons by in situ combustion



March 15, 1966 J. w. MARX RECOVERY OF HYDROCARBONS BY IN SITU COMBUSTION Filed May 2, 1958 INVENTOR.

J.W. MARX BY if ATTORNEYS WATE R TO STORAGE United States Patent 3,240,270 RECOVERY OF HYDROCARBONS BY IN SlTU COMBUSTION John W. Marx, Bartlesville, Okla, assiguor to Phillips Petroleum Company, a corporation of Delaware Filed May 2, 1958, Ser. No. 732,730 17 Claims. (Cl. 166-4) This application is a continuation-in-part of application S.N. 526,388 filed August 4, 1955, now abandoned, wherein it is disclosed that producing a stratum by inverse in situ combustion substantially refines and upgrades the original hydrocarbon material, rendering the same substantially less viscous.

This invention relates to an improved method for the recovery of hydrocarbons by in situ combustion in a carbonaceous stratum. A specific aspect of the invention is concerned with the prevention of combustion of hydrocarbon products in a production borehole.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in the stratum is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this diffculty and to permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

In field tests in which hydrocarbons were recovered by in situ combustion in a tar sand by inverse air injection it was found that a material proportion of the injected air by-passed the combustion front and appeared in the production borehole along with produced hydrocarbons. Even in the ignited zones, air is believed to by-pass the fire front because of thermal fracturing which provides some channeling therethru. The by-passed oxygen mixes with the combustible products from the burning zones and appears in the production well which is generally above the ignition temperature of the hydrocarbon-oxygen mixture when this happens, and field tests to date indicate, as a rule rather than the exception, that the mixture burns in the production borehole and production tubing unless suitable precautions are taken Temperatures in excess of 2500 F. have been frequently observed in a production borehole from this cause. This temperature has been more than sufiicicnt to melt downhole equipment on several occasions. Furthermore, if the by-passed oxygen quantity is large, it may consume the entire product, thereby rendering the process entirely useless. In addition, serious personnel hazards are created.

Accordingly, it is an object of the invention to provide an improved process for recovering hydrocarbons by in situ combustion in a carbonaceous stratum. Another object is to provide a process for preventing combustion in a production borehole during recovery of hydrocarbons by in situ combustion. A further object is to prevent production borehole fires in an inverse air injection in situ combustion process for recovery of hydrocarbons from a carbonaceous stratum. It is also an ob ject of the invention to provide a process for controlling the temperature in a production borehole in an inverse air injection in situ combustion process. Other objects will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises an improved in situ combustion process for the recovery of hydrocarbons from. a carbonaceous stratum wherein a combustion front is established around one or more wall bores in the stratum and the front is moved thru the stratum by feeding O thereto, with produced hydrocarbons being recovered along with combustion gas thru one or more production boreholes in the stratum, wherein O by-passes the combustion front and appears in the gases in the production boreholes so as to create borehole fires, the improvement comprising injecting an inert cooling fluid into the production boreholes so as to maintain the temperature therein below combustion supporting temperature at the 0 concentration therein and prevent borehole fires. The preferred and most advantageous cooling fluid is H O in liquid form and/ or steam form, but other coolants inert in the well bore ambient and readily separable from the production eflluent may be utilized. Such coolants include N CO combustion gases, etc. The ensuing description of the invention will be limited to H O as the coolant but it is to be understood that other coolants may be utilized, even tho less advantageously,

A more complete and comprehensive understanding of the invention may be had by reference to the accompanying schematic drawing which is an elevation in partial section showing an arrangement of apparatus in a borehole thru a carbonaceous stratum illustrating the invention.

Referring to the drawing, a borehole 10 penetrates a carbonaceous stratum 12 and is provided with a casing 14, extending from ground level to the upper level of the stratum, and with production tubing 16, extending from the lower end of the casing thru well head 18 to separating menas 20. Line 22 carries water from separator 20 to waste or to recycle to the process as desired. Line 24 carries recovered hydrocarbons to storage facilities.

A water line 26 extends to a level in casing 14 adjacent the lower end of tubing 16 and is provided with a spray head or nozzle 28. Water line 26 passes thru well head 18 and connects with a supply source, such as water tank 30. A pump 32 is inserted in line 26 for providing the desired pressure at spray head 28. Motor valve 34 is positioned in line 26 downstream of pump 32. Thermocouple 36, positioned in the well bore adjacent the lower end of production tubing 16 and preferably just above the level of spray nozzle 28, is connected with a temperature-recorder-controller 38 which is in operative control of motor valve 34.

At the stage of the process illustrated in the drawing, the fire front 40 has advanced from borehole 10 thru the stratum a substantial distance toward surrounding air injection boreholes not shown. The product hydrocarbons pass thru the burned out area intermediate fire front 40 and borehole 10 to the borehole and into production tubing 16 in conventional manner. Fire front 40 eventually progresses to the injection boreholes and upon arrival, with continued air injection, the front is reversed in direction and is driven back to borehole 10 by direct air drive, feeding upon the carbonized residue left in the stratum during the inverse air injection phase of the process.

During the inverse air injection phase of the process, the hydrocarbons produced in and around fire front 40 by the heat of the combustion process and the flushing action of the combustion gases, principally in vapor form, pass into the borehole 10 at elevated temperatures around 1000 F. and sometimes as high as 1500 or 1600 F. In this type of in situ combustion, the produced hydrocarbons passing thru the hot burned out zone back of the combustion front and which by-passes the fire front appear in admixture in the production borehole and the temperature of the mixture sustains combustion, so that all of the oxygen present in borehole consumes hydrocarbons and to that extent destroys valuable products, as well as contributing to excessive temperatures and damage to downhole equipment.

During the direct drive of the combustion front from the injection wells back to the production well, the front travels thru the still hot burned out stratum and by passed oxygen is again present in the well bore in admixture with hot hydrocarbons thereby causing borehole fires. The present invention prevents borehole fires or, if a borehole fire develops, the process can be utilized to extinguish the same and prevent the occurrence of further borehole combustion.

In operation of the invention, water is sprayed into the borehole, preferably, under substantial pressure such as 30 to 90 p.s.i.g., thru a downhole spray, such as spray 28, so as to maintain the temperature in the borehole in the stratum below combustion supporting temperature at the concentration of oxygen in the borehole. It has been found that borehole fires do not occur when the temperature of the borehole is maintained below about 750 F. and it is preferable to control the injection of water into the borehole so as to maintain the temperature in the range of about 600 to about 700 F., altho temperatures as low as 500 and as high as 750 have been used successfully. At higher temperatures, particularly at higher concentrations of oxygen, fire develops in the borehole and destroys valuable hydrocarbons being produced. As the temperature in the borehole drops below about 500 F., liquid products accumulate in the bottom of the borehole and water injected into the boreholeforms an emulsion therewith which greatly complicates the separation problem in separator 20. In addition, at lower borehole temperatures the water hydrocarbon emulsion in the bottom of the borehole is agitated by the flow of gases into the borehole and considerable erosion of the borehole wall below casing 14 occurs, with substantial amounts of sand and eroded material from the borehole appearing in the production efiiuent, further complicating the separation process. In other respects, at temperatures below 500 F., the process is just as effective in preventing borehole fires and preserving valuable hydrocarbons, but operation in this manner introduces other problems and disadvantages to the process which are undesirable.

While it is preferred to inject water in the manner shown in the drawing it has also been found effective to merely spray or otherwise inject water into the mouth of the borehole at ground level, whereby the water descends by gravity into the hot downhole section of the borehole where it effectively cools the production efiluent so as to prevent the combustion of hydrocarbons with by-passed oxygen and thereby avoids well bore fires.

A preferred method of operation comprises sensing the temperature adjacent the upper level of the stratum being produced by means of thermocouple 36, or other tem perature sensing device, which is connected with a temperature-recorder-controller 38 which in turn is connected with motor valve 34 and thereby controls the opening of valve 34 so as to inject the required amount of water into the borehole to maintain the temperature below the set temperature of instrument 38. While this is the preferred method of operating the process, hand operation of a flow control valve in line 26 in response to a sensing temperature in the well bore adjacent to the producing stratum has been found satisfactory in a number of well tests. It is not necessary that the injection of water be continuous, as intermittent injection of water has been successfully tested.

Field tests in inverse air injection in situ combustion in a tar sand of substantial thickness at a level between 50 and feet below the surface extending over a period of several months have been completed utilizing injection of water into the production boreholes at various levels in the well bore both intermittently and continuously. The injection of water in the manner described was found to be completely effective in eliminating borehole fires when the temperature was maintained below the range of 700 to 750 F. It was found that when as low a concentration of oxygen in the production well bore as 0.5 volume percent occurred, the temperature in the well' bore rose from about 1000 F. to the range of 1500 to 1600 F., without injection of water into the borehole, and with an oxygen concentration of only 3.0 percent, the temperature rose to at least 2500 F. Oil production without borehole combustion was sustained in some of these tests in which as much as percent of the injected air by-passed the fire front and where the noncondensible effluent gas contained more than 18 percent oxygen. It was surprising that the critical maximum borehole temperature was as high as the range of 700 to 750 F. and that operation at borehole temperatures below about 500 F. was so undesirable because of complicating problems resulting therefrom.

A preferred method of initiating in situ combustion in and around the ignition or production borehole in an inverse burning process comprises heating the wall of the borehole within the carbonaceous stratum to ignition temperature and, while at this temperature, passing airthru the statum into the borehole from one or more surrounding injection boreholes so as to initiate combustion of the carbonaceous material in the stratum. Thereafter, continued passage of air thru the stratum to the ignition borehole causes the resulting combustion zone or front to move thru the statum countercurrently to the injected air. It is advantageous to incorporate a small per cent fuel gas, such as 1 to 2% propane, with the injected air while initiating in situ combustion.

While the simplest method of injecting water into the hot production borehole within the stratum is thru a water line leading into the borehole and, preferably, to.

a level just above the stratum, it is also feasible to inject water into the borehole, or its wall, from one or more boreholes in the stratum within a short radius, such as one to several feet from the production borehole. Water injected in this manner into the wall of the production borehole has the beneficial cooling and diluting effect but requires drilling extra boreholes and is less desirable for this reason.

While the foregoing description of the invention is limited to fluid coolants, it is feasible to use readily vaporizable solid coolants such as particulate solid CO (Dry Ice) or ordinary ice, although the problem of introducing these materials to the well bore is a factor to be considered which makes injection of liquid H O or gaseous CO preferable.

It has been found in inverse air injection field tests that the rate of air injection must be at least about 20 standard cubic feet per square foot of combustion front per hour in order to sustain a combustion front moving inversely to the air flow. When the air injection rate is reduced below this minimum, the combustion front is either reversed in direction, so as to burn back to the production borehole, or the fire goes out. The upper limit of the air injection rate depends upon economic factors such as compressor loss, consumption of valuable hydrocarbons in the stratum, and the character of the carbonaceous stratum itself; however, air rates of about 50 standard cubic feet per square foot of fire front per hour are marginal and can be economically utilized, while air rates of 100 s.c.f.h. per square foot of fire front are generally uneconomical and are maximum in any type of stratum.

Certain modifications of the invention become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

1 claim:

1. A process for refining and upgrading hydrocarbons in situ in a carbonaceous stratum and recovering the resulting hydrocarbons which comprises establishing a combustion zone around a production borehole in said stratum by heating same to ignition temperature and contacting the hot stratum with 0 moving said zone thru said stratum by injecting 0 containing, combustionsupporting gas into said stratum thru at least one other borehole therein, whereby the combustion zone moves oountercurrently to the flow of said gas and hydrocarbon material in place in said stratum is driven thru the hot burned over stratum behind the combustion zone so as to refine and upgrade the same and whereby a portion of the O injected into the stratum for combustion purposes by-passes the combustion zone and appears in the production borehole in admixture with upgraded hydrocarbons; injecting 'a fluid coolant inert in the production borehole ambient directly into said production borehole so as to mix said coolant with the produced gases therein and prevent reaction between the bypassed O and produced hydrocarbons in said production borehole; recovering the upgraded and refined hydrocarbons from said production borehole in admixture with said coolant, O and combustion gas; and recovering said hydrocarbons from said admixture.

2. The process of claim 1 wherein the injected coolant comprises H 0.

3. The process of claim 1 wherein said coolant is H 0 and same is injected into the produced gases adjacent said stratum.

4. A process for producing hydrocarbons from a carbonaceous stratum penetrated by an ignition borehole and an offset borehole which comprises heating and igniting said stratum adjacent said ignition borehole with O to establish a combustion front; feeding 0 into said stratum and into said front thru one of said boreholes and producing hydrocarbons thru the other of said boreholes as a production borehole so as to move said front toward said offset borehole, whereby some of said 0 by-passes said front and appears in the produced hydrocarbons in said other of said boreholes, normally burning a portion of the hydrocarbons therein; injecting an inert fluid coolant directly into the produced gases in said production borehole adjacent said stratum in direct heat exchange with said gases so as to maintain the temperature of the produced hydrocarbons within said production borehole below the ignition temperature thereof and prevent borehole fire; and withdrawing said coolant with the produced hydrocarbons from said production borehole.

5. The process of claim 4 wherein air is injected into said stratum thru said offset borehole to feed 0 into said front and water is sprayed into said production borehole as said coolant.

6. The process of claim 5 wherein said front is established by heating said stratum adjacent said production borehole to ignition temperature of the carbonaceous material in the wall thereof and, while at said temperature, injecting 0 thru said ignition borehole to ignite the hot material in the wall of said production borehole.

7. The process of claim 5 wherein said front is established by heating said production borehole to ignition temperature of carbonaceous material in the wall thereof and while at said temperature injecting 'air containing a low concentration of fuel gas thru said offset borehole and thru said stratum into said production borehole so as to ignite said material.

8. The process of claim 4 wherein H O is injected as said coolant intermittently into said production borehole as the temperature therein reaches the range of about 650 to 750 F.

9. The process of claim 4 wherein H 0 is injected as said coolant continuously into said production borehole so as to maintain the temperature therein below 750 F.

10. The process of claim 4 wherein said coolant is H O in liquid form.

11. The process of claim 4 wherein said coolant is H O in vapor form.

12. The process of claim 4 wherein said temperature is maintained in the range of 500 to 750 F.

13. The process of claim 12 utilizing water as the coolant.

14. The process of claim 4 utilizing water as the coolant wherein the temperature in the production well bore at a point adjacent said stratum is sensed and the flow of water is controlled in response to said temperature so as to maintain same in the range of about 500 to 750 F.

15. The process of claim 14 wherein water is sprayed downwardly into the well bore at a level adjacent the upper level of said stratum but below the temperature sensing point.

16. In a process for producing hydrocarbons from a carbonaceous stratum penetrated by an ignition borehole and an offset borehole which comprises heating said stratum to ignition temperature and igniting said stratum adjacent said ignition borehole in the presence of a combustion supporting gas to establish a combustion front, feeding said gas into said stratum and into said front through one of said boreholes and producing hydrocarbon fluids through the other of said boreholes as a production borehole so as to move said front toward said offset borehole, injecting an inert fluid coolant into said production borehole and contacting the produced fluids therewith adjacent said stratum so as to maintain the temperature of the produced hydrocarbon fluids within said production borehole below the ignition temperature thereof and prevent borehole fire; and withdrawing said coolant and the produced hydrocarbon fluids from said production borehole.

17. In a process for producing hydrocarbons from a carbonaceous stratum penetrated by an ignition borehole and an offset borehole which comprises igniting said stratum adjacent said ignition borehole in the presence of a combustion supporting gas to establish a combustion front, feeding said gas into said stratum and into said front through one of said boreholes and producing hydrocarbon fluids through the other of said boreholes as a production borehole so as to move said front toward said offset borehole, injecting an inert fluid coolant into said production borehole and contacting said produced fluids therewith adjacent said stratum so as to maintain the temperature of the produced fluids within said production borehole below the ignition temperature thereof and prevent borehole fire; and withdrawing said coolant and 7 The produced hydrocarbon fluids from :said production 2,793,696 borehole. 2,877,847 2,880,803 References Cited by the Examiner UNITED STATES PATENTS 5 481,151

1,552,342 9/1925 Porter 16690 2,734,579 2/1956 Elkins 16611 2,788,071 4/1957 Pelzer 16611 5/1957 Morse 166-11 3/1959 =P'e1zer 16639 4/1959 Parker 166-11 FOREIGN PATENTS 2/1952 Canada.

CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN BENDETT, Examiner. 

17. IN A PROCESS FOR PRODUCING HYDROCARBONS FROM A CARBONACEOUS STRATUM PENETRTED BY AN IGNUTUIN BOREHOLE AND AN OFFSET BOREHOLE WHICH COMPRISES IGNITING SAID STRATUM ADJACENT SAID IGNITION BOREHOLE IN THE PRESENCE OF A COMBUSTION SUPPORTING GAS TO ESTABLISH A COMBUSTION FRONT, FEEDING SAID GAS INTO SAID STRATUM AND INTO SAID FRONT THROUGH ONE OF SAID BOREHOLES ND PRODUCING HYDROCARBON FLUIDS THROUGH THE OTHER OF SAID BOREHOLES AS A PRODUCTION BOREHOLE SO AS TO MOVE SAID FRONT TOWARD SAID OFFSET BOREHOLE, INJECTING AN INERT FLUID COOLANT INTO SAID PRODUCTION BOREHOLE AND CONTACTING SAID PRODUCED FLUIDS THEREWITH ADJACENT SAID STRTUM SO AS TO MAINTAIN THE TEMPERATURE OF THE PRODUCED FLUIDS WITHIN SAID PRODUCTION BOREHOLE BELOW THE IGNITION TEMPERATURE THEREOF AND 